Communication systems, such as cellular systems (both time division multiple access (TDMA) and code division multiple access (CDMA) cellular systems) and personal communication systems (PCS), typically include mobile units and infrastructure, such as base stations, with which the mobile units communicate. The infrastructure links the mobile units to a land line telephone system such as, for example, a point switched telephone network (PSTN) to enable mobile unit users to communicate with land line users. For example, when a mobile unit user places a call to a person at a land line telephone, the infrastructure connects the mobile unit to the land line.
Typically, mobile units are compact and battery powered so that they are easily transportable. For example, a user may carry a mobile unit in her purse, pocket, briefcase or car. While mobile units may have access to external power sources in some situations (e.g., in a car through the use of a lighter adapter), mobile units do not always have access to power other than their own self contained batteries. In a typical use, a user may charge the battery of her mobile unit over the weekend and, on Monday morning, may turn the mobile unit on and put it in her purse. Thereafter, the user may not recharge the battery until the mobile unit gives her a low battery indication. When the mobile unit is turned on and the user is not using the mobile unit for a call, the mobile unit is in standby. While in standby, a mobile unit cycles through a number of operating modes. For example, while in standby, a mobile unit may cycle through or between a sleep mode that draws very little current, various setup and power up modes that draw more current than the sleep mode and a full receive mode, wherein the mobile unit's receiver is fully powered up and is looking for communications, such as pages, from the infrastructure. In standby, the mobile unit occasionally looks for communication signals from the infrastructure, which would alert the mobile unit that the infrastructure is passing a call to the mobile unit. Standby is one of the most common operating modes for a mobile unit and commonly mobile unit manufacturers specify the standby battery life of their mobile units for a particular battery size.
Because standby is one of the most common modes of mobile unit operation, it will be readily appreciated that battery life in standby is a critical mobile unit feature. Battery life in standby mode is inversely proportional to the current that a mobile unit draws from its battery during standby operation. With the goal of extending standby times as far as possible, various semiconductor and mobile unit manufacturers have developed electrical components (e.g., chip sets or semiconductors) having various sections of circuitry that may be independently powered down. Such components allow, for example, transmitter circuitry, which is not needed in standby, to be powered down, thereby reducing the current consumption of the mobile unit by the amount of current saved by powering down the transmitter circuitry.